The objective of this project is to explore the genetic variants of glucose-6phosphate dehydrogenase (G-6-PD) with particular reference to those that occur with sufficient frequency in a population to suggest a balanced polymorphism. Specific aim No. 1 is to determine the clinical effects of the more common G-6-PD variants. Specific aim No. 2 is to determine the geographic distribution of the major variants. Specific aim No. 3 is to purify completely and to analyze structurally G-6-PD variants.